EXTERNAL HEAT SINK FOR BARE-DIE FLIP CHIP PACKAGES
An integrated circuit package includes a substrate having opposing first and second surfaces, a flip chip integrated circuit die, and a heat sink. A first surface of die is mounted to the first surface of the substrate by a plurality of electrically conductive solder bumps. The heat sink has a first surface that includes a recessed region extending along a length of the heat sink in the first surface and that includes first and second supporting portions separated by the recessed region. The first and second supporting portions are attached to the first surface of the substrate such that the die is positioned in the recessed region. A second surface of the die is attached to a surface of the recessed region.
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This application claims the benefit of U.S. Provisional Application No. 61/083,225, filed on Jul. 24, 2008, which is incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to integrated circuit packaging technology, and more particularly to flip chip integrated circuit package substrates.
2. Background Art
Integrated circuit (IC) chips or dies from semiconductor wafers are typically interfaced with other circuits using a package that can be attached to a printed circuit board (PCB). One such type of IC die package is a ball grid array (BGA) package. BGA packages provide for smaller footprints than many other package solutions available today. A BGA package has an array of solder ball pads located on a bottom external surface of a package substrate. Solder balls are attached to the solder ball pads. The solder balls are reflowed to attach the package to the PCB.
In some BGA packages, a die is attached to the substrate of the package (e.g., using an adhesive), and signals of the die are interfaced with electrical features (e.g., bond fingers) of the substrate using wire bonds. In such a BGA package, wire bonds are connected between signal pads/terminals of the die and electrical features of the substrate. In another type of BGA package, which may be referred to as a “flip chip package,” a die may be attached to the substrate of the package in a “flip chip” orientation. In such a BGA package, solder bumps are formed on the signal pads/terminals of the die, and the die is inverted (“flipped”) and attached to the substrate by reflowing the solder bumps so that they attach to corresponding pads on the surface of the substrate.
The dies in integrated circuit packages, such as BGA packages, typically generate a great amount of heat during operation. Thus, BGA packages are frequently configured to disperse the generated heat so that their operation is not adversely affected by the generated heat. For example, an external heat sink may be attached to a BGA package to disperse heat from the BGA package. External heat sinks are effective solutions to improving the thermal performance of a package. However, in the case of flip chip BGA packages, the package geometry creates additional complexities in the mounting of such heat sinks.
For instance, most existing external heat sinks utilize a solid base plate design that is completely flat on the bottom surface. The flat base plate surface serves as an interface between the heat sink and the package, and can be used reliably on plastic BGA packages and flip-chip BGA packages that already have a heat spreader “lid” included. Complications arise when the external heat sink is mounted on a bare die flip-chip package, in which the relatively large external heat sink rests solely on the relatively small silicon die of the package. This creates a high amount of stress on the die, which may lead to damage to the die or the interconnect between the die and the flip chip substrate, rendering the package useless. In such a configuration, stability is another problem. Because the heat sink only has support in the center, the heat sink can easily be dislodged if a moment is applied. Conventional solutions for these problems increase an overall cost such that a flip chip BGA-plus-heat spreader (e.g., a BGA package that has a heat spreader lid attached) package becomes a more cost-efficient option than a bare die flip chip BGA package.
BRIEF SUMMARY OF THE INVENTIONIntegrated circuit packages, heat sinks, and methods and systems for assembling the same are provided.
In one implementation, an integrated circuit package includes a substrate having opposing first and second surfaces, a flip chip integrated circuit die, and a heat sink. A first surface of the die is mounted to the first surface of the substrate by a plurality of electrically conductive solder bumps. The heat sink has a first surface that includes a recessed region extending along a length of the heat sink in the first surface and that includes first and second supporting portions separated by the recessed region. The first and second supporting portions are attached to the first surface of the substrate such that the die is positioned in the recessed region. A second surface of the die is attached to a surface of the recessed region.
In another implementation, an integrated circuit package includes a substrate having opposing first and second surfaces, a flip chip integrated circuit die, and a heat sink. The flip chip integrated circuit die has opposing first and second surfaces. The first surface of the die is mounted to the first surface of the substrate by a plurality of electrically conductive solder bumps. The heat sink has a first surface that includes a first post extending from a first corner of the first surface of the heat sink, a second post extending from a second corner of the first surface of the heat sink, a third post extending from a third corner of the first surface of the heat sink, and a fourth post extending from a fourth corner of the first surface of the heat sink. The first, second, third, and fourth posts are attached to the first surface of the substrate such that the die is positioned within a perimeter formed by the first, second, third, and fourth posts, and the second surface of the die is attached to the first surface of the heat sink.
In another implementation, a method for assembling integrated circuit packages is provided. A stock material is extruded through an extrusion die to form a heat sink strip having a cross-section defined by the extrusion die. The extruding includes forming a recessed region in a first surface of the heat sink strip that extends along a length of the heat sink strip, and forming a plurality of fins in a second surface of the heat sink strip along the length of the heat sink strip. The heat sink strip is cross-cut to separate the heat sink strip into a plurality of heat sinks.
In still another implementation, a system for assembling integrated circuit packages is provided. The system includes an extrusion press and a cross-cutter. The extrusion press is configured to extrude a stock material through an extrusion die to form a heat sink strip having a cross-section defined by the extrusion die. The extrusion die is configured to form a recessed region in a first surface of the heat sink strip along a length of the heat sink strip, and to form a plurality of fins in a second surface of the heat sink strip along the length of the heat sink strip. The cross-cutter is configured to cross-cut the heat sink strip to separate the heat sink strip into a plurality of heat sinks.
These and other objects, advantages and features will become readily apparent in view of the following detailed description of the invention. Note that the Summary and Abstract sections may set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s).
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
DETAILED DESCRIPTION OF THE INVENTION IntroductionThe present specification discloses one or more embodiments that incorporate the features of the invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.
References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Furthermore, it should be understood that spatial descriptions (e.g., “above,” “below,” “up,” “left,” “right,” “down,” “top,” “bottom,” “vertical,” “horizontal,” etc.) used herein are for purposes of illustration only, and that practical implementations of the structures described herein can be spatially arranged in any orientation or manner.
Example Integrated Circuit PackagesExample integrated circuit packages are described in this section.
Substrate 104 may include one or more electrically conductive layers (such as at first surface 112) that are separated by one or more electrically insulating layers. An electrically conductive layer may include traces/routing, bond fingers, contact pads, and/or other electrically conductive features. For example, BGA substrates having one electrically conductive layer, two electrically conductive layers, or four electrically conductive layers are common. The electrically conductive layers may be made from an electrically conductive material, such as a metal or combination of metals/alloy, including copper, aluminum, tin, nickel, gold, silver, etc. In embodiments, substrate 104 may be rigid or may be flexible (e.g., a “flex” substrate). The electrically insulating layer(s) may be made from ceramic, plastic, tape, and/or other suitable materials. For example, the electrically insulating layer(s) of substrate 104 may be made from an organic material such as BT (bismaleimide triazine) laminate/resin, a flexible tape material such as polyimide, a flame retardant fiberglass composite substrate board material (e.g., FR-4), etc. The electrically conductive and non-conductive layers can be stacked and laminated together, or otherwise attached to each other, to form substrate 104, in a manner as would be known to persons skilled in the relevant art(s).
As shown in
Underfill material 118 may be optionally present, as shown in
A plurality of solder balls 108 (including solder balls 108a and 108b indicated in
Packages 500 and 600 shown in
Packages 900 and 1000 have some benefits. For example, packages 900 and 1000 exhibit relatively good thermal performance. Relatively large heat sinks can be mounted to heat spreader plate 704 (shown in
Ring gasket 1104 is a soft, adhesive ring gasket which may be used to prevent the external heat sink (e.g., heat sink 502) from rocking back and forth when the heat sink is mounted on a bare die 102 (e.g., as shown in
Stiffener ring 1302, which may be copper, for example, has a thickness generally equal to a combined thickness of die 102 and bumps 106 (e.g., as shown in
Studs 1402 provide additional support when mounting an external heat sink (e.g., heat sink 502 shown in
Example embodiments are described in the following section that overcome deficiencies of the flip chip BGA package and heat sink configurations described above.
EXAMPLE EMBODIMENTSThe example embodiments described herein are provided for illustrative purposes, and are not limiting. Although described below with reference to BGA packages, the examples described herein may be adapted to other types of integrated circuit packages. Including pin grid array (PGA) (e.g., a package having pins for package mounting), land grid array (LGA) (e.g., a package having pads for package mounting), and further types of integrated circuit packages that include one or more dies mounted to a substrate. Furthermore, additional structural and operational embodiments, including modifications/alterations, will become apparent to persons skilled in the relevant art(s) from the teachings herein.
Extrusion and cross-cut extrusion external heat sinks for bare-die flip-chip BGA applications are provided. External heat sinks improve the thermal performance of a flip chip BGA packages. However, the geometry of bare-die flip-chip BGA packages creates additional complexities in the mounting of such heat sinks. Embodiments for heat sinks and BGA packages described herein avoid such complexities without causing significant additional cost. In an embodiment, a heat sink base plate portion includes a recessed region that encloses the die on a package substrate. Both the top of the die and the top of the substrate may be in contact with the base plate portion of the heat sink, creating a stable structure that provides high thermal performance.
To overcome reliability, stability, and/or cost issues in mounting an external heat sink to a bare-die flip-chip BGA package, instead of using a base plate having a planar bottom surface, the base plate is manufactured to have a recessed region near or at the center of the base plate along the length of the base plate. The recessed region may have a height/depth that is substantially the same as the height of a die (plus underfill bumps). An example of a typical recessed region height provided for illustrative purposes may be 0.85 mm, or the recessed region may have any other suitable height. Such a base plate provides mechanical advantages, including a support structure that meets the substrate near the edges of the heat sink, and a recessed region to meet the height of the die near the center of the heat sink. A groove-like or bridge-like structure is created over the die that allows the heat sink to be in contact with the package at the substrate and the die. Such a configuration may be referred to as a “grooved heat sink” or “bridged heat sink.”
The size of the recessed region in the heat sink may be selected based on the particular heat sink application. For example, the recessed region size may be selected to be larger than a size of the die to be enclosed in the recessed region. In an embodiment, the width of the package equal to or wider than the distance between the outer edges of the heat sink support structures (the edges of the heat sink on either side of the recessed region). In another embodiment, the width of the package may be less than the distance between the outer edges of the heat sink support structures.
In an embodiment, a heat sink is configured to accommodate packages having a footprint equal to or greater than an area of the heat sink. In another embodiment, a heat sink is configured to be securely mounted on packages that have a footprint that may be smaller than an area of the heat sink. In further embodiments, a configuration of the heat sink directs airflow to the die. For example, air may be able to flow through the package by flowing over the substrate, along the sides of the die through the groove formed by the heat sink.
In an embodiment, extrusion or cross-cut extrusion manufacturing techniques may be used to manufacture heat sinks. A bridge shape of a heat sink base plate can be formed during an extrusion process, in which the bridge shaped feature will be included in the heat sink forming die (a die used for extrusion—“extrusion die”—not to be confused with the package semiconductor die). Cost-effective manufacturing processes that are already in place may be taken advantage of so that additional steps to the heat sink forming process are not needed.
As compared to flip chip BGA packages having external heat sinks (without heat sink mounts), such as shown in
As compared to flip chip BGA packages having external heat sinks, grooved heat sink embodiments provide advantages. For example, a bridged heat sink offers similar mechanical advantages to the heat sink mounting solutions described above with respect to
Various example embodiments of bridged heat sinks are described in further detail below.
For example,
Several example dimensions for heat sink 1600 are shown in
Several example dimensions for heat sink 1800 are shown in
Several example dimensions for heat sink 1900 are shown in
As shown in
Cavity 2004 may have any suitable width and depth configured to accommodate one or more components 2006 mounted to substrate 104. Furthermore, any number of cavities 2004 may be present in heat sink 2002, as required for a particular application. For example,
Bridged heat sinks may be formed in a variety of ways, according to embodiments of the present invention. For example,
As shown in
Forcing stock material 2208 through die 2206 generates a heat sink strip 2210, which has a cross-section defined by die 2206. Thus, extrusion press 2202 may form features in heat sink strip 2210, such as fans (such as fans 1504 shown in
For instance,
In step 2304, the heat sink strip is cross-cut to form a plurality of heat sinks. For example, with reference to
Note that system 2200 of
Note that system 2200 shown in
Die-to-substrate mounter 3202 receives dies 3206 and substrates 3208. Substrates 3208 may be received individually or in the form of a strip of substrates. Die-to-substrate mounter 3202 is configured to perform the step of mounting dies 3206 to substrates 3208. For example, die-to-substrate mounter 3202 may include a pick-and-place machine or other mechanism used to mount individual dies to substrates. Solder bumps and/or solder balls may be reflowed to attach the dies to the substrates in a flip chip manner, and an underfill material may be optionally applied. Die-to-substrate mounter 3202 outputs die-mounted substrates 3210.
As described above, extrusion press 2202 may extrude stock material 2208 to form heat sink strip 2210, according to step 2302 of flowchart 2300 (
Heat sink-to-substrate attacher 3204 may receive die-mounted substrates 3210 and heat sinks 2212, and may attach heat sinks 2212 to die-mounted substrates 3210 as described above. For example, heat sink-to-substrate attacher 3204 may include a pick-and-place machine or other mechanism used to mount individual heat sinks to substrates. Heat sink-to-substrate attacher 3204 outputs heat sink and die-mounted substrates 3214.
Interconnect attacher 2210 may receive heat sink and die-mounted substrates 3214, and attach or form solder balls or other electrical interconnect on the substrates, and may output integrated circuit packages 3216.
Note that in another embodiment, if the dies are mounted to a substrate strip by die-to-substrate mounter 3202, the die-mounted substrate strip may be singulated into separate substrates/integrated circuit packages at any point in system 3200. For example, in an embodiment, cross-cutter 2204 may be positioned in system 3200 after heat sink-to-substrate attacher 3204. Heat sink strip 2210 may be attached to a die-mounted substrate strip by heat sink-to-substrate attacher 3204, and cross-cutter 2204 may subsequently be used to singulate the substrate strip into separate substrates, simultaneously cutting heat sink strip 2210 into separate heat sinks.
CONCLUSIONWhile various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents
Claims
1. A method for assembling integrated circuit packages, comprising:
- extruding a stock material through a die to form a heat sink strip having a cross-section defined by the die, said extruding comprising forming a recessed region in a first surface of the heat sink strip that extends along a length of the heat sink strip, and forming a plurality of fins in a second surface of the heat sink strip along the length of the heat sink strip; and
- cross-cutting the heat sink strip to separate the heat sink strip into a plurality of heat sinks.
2. The method of claim 1, further comprising:
- forming a plurality of cross-cuts in the second surface of the heat sink strip across a width of the heat sink strip such that each heat sink separated from the heat sink strip includes a plurality of rows of fins, each row of the plurality of rows including multiple fins.
3. The method of claim 1, further comprising:
- forming a cavity in the recessed region of at least one heat sink of the plurality of heat sinks.
4. The method of claim 1, wherein said extruding further comprises:
- forming a notch in a side surface of the heat sink strip that extends along the length of the heat sink strip.
5. The method of claim 1, wherein said forming a plurality of fins in a second surface of the heat sink strip along the length of the heat sink strip comprises:
- forming a first fin that is located opposite the recessed region to be offset from a second fin adjacent to the first fin.
6. The method of claim 1, wherein said extruding further comprises:
- forming a second plurality of fins in the recessed region that extends from the first surface of the heat sink strip and that is opposed to the first plurality of fins.
7. The method of claim 1, wherein said extruding further comprises:
- forming first and second protruding portions separated by the recessed region and extending along the length of the heat sink strip to be offset from outer edges of the width of the heat sink strip.
8. The method of claim 1, further comprising:
- forming a plurality of cross-cuts in the second surface of the heat sink strip across a width of the heat sink strip such that each heat sink separated from the heat sink strip includes a first post extending from a first corner of the heat sink, a second post extending from a second corner of the heat sink, a third post extending from a third corner of the heat sink, and a fourth post extending from a fourth corner of the heat sink.
9. The method of claim 8, further comprising:
- forming a rectangular cavity in the recessed region of at least one heat sink of the plurality of heat sinks.
10. The method of claim 9, wherein said forming a rectangular cavity in the recessed region of at least one heat sink of the plurality of heat sinks comprises:
- forming the cavity such that each corner of the cavity is adjacent to an inner corner of a corresponding one of the first, second, third, and fourth posts of the at least one heat sink.
11. The method of claim 9, wherein said forming a rectangular cavity in the recessed region of at least one heat sink of the plurality of heat sinks comprises:
- forming the cavity to form a notch in each of the first, second, third, and fourth posts of the at least one heat sink.
12. The method of claim 8, wherein said forming a plurality of cross-cuts in the second surface of the heat sink strip comprises:
- forming the plurality of cross-cuts to have a depth that is less than a depth of the recessed region.
13. An integrated circuit package, comprising:
- a substrate having opposing first and second surfaces;
- a flip chip integrated circuit die having opposing first and second surfaces, wherein the first surface of the die is mounted to the first surface of the substrate by a plurality of electrically conductive solder bumps; and
- a heat sink having a first surface that includes a recessed region extending along a length of the heat sink in the first surface and that includes first and second supporting portions separated by the recessed region, wherein the first and second supporting portions are attached to the first surface of the substrate such that the die is positioned in the recessed region, and the second surface of the die is attached to a surface of the recessed region.
14. The integrated circuit package of claim 13, wherein the heat sink has a second surface that is opposed to the first surface of the heat sink, wherein the heat sink further includes a plurality of fins extending from the second surface.
15. The integrated circuit package of claim 14, wherein each fin extends along the length of the heat sink.
16. The integrated circuit package of claim 14, wherein the plurality of fins are formed in a plurality of rows, and each row of the plurality of rows includes multiple fins.
17. The integrated circuit package of claim 13, further comprising:
- an electrical component mounted to the first surface of the substrate, the electrical component having a height greater than a height of the die;
- wherein the surface of the recessed region includes a cavity, wherein a portion of the electrical component extends into the cavity.
18. The integrated circuit package of claim 13, wherein the heat sink includes a notch in a side surface of the heat sink that extends along the length of the heat sink.
19. The integrated circuit package of claim 14, wherein at least one fin of the plurality of fins is offset from an adjacent fin of the plurality of fins.
20. The integrated circuit package of claim 14, wherein the recessed region of the heat sink includes a second plurality of fins extending from the first surface of the heat sink and that is opposed to the first plurality of fins, wherein each fin of the second plurality of fins extends along the length of the heat sink.
21. The integrated circuit package of claim 13, wherein the first and second supporting portions are offset from outer edges of the width of the first surface of the heat sink.
22. The integrated circuit package of claim 13, further comprising:
- a first post extending from the first supporting portion at a first corner of the heat sink;
- a second post extending from the first supporting portion at a second corner of the heat sink;
- a third post extending from the second supporting portion at a third corner of the heat sink; and
- a fourth post extending from the second supporting portion at a fourth corner of the heat sink.
23. An integrated circuit package, comprising:
- a substrate having opposing first and second surfaces;
- a flip chip integrated circuit die having opposing first and second surfaces, wherein the first surface of the die is mounted to the first surface of the substrate by a plurality of electrically conductive solder bumps; and
- a heat sink having a first surface that includes a first post extending from a first corner of the first surface of the heat sink, a second post extending from a second corner of the first surface of the heat sink, a third post extending from a third corner of the first surface of the heat sink, and a fourth post extending from a fourth corner of the first surface of the heat sink;
- wherein the first, second, third, and fourth posts are attached to the first surface of the substrate such that the die is positioned within a perimeter formed by the first, second, third, and fourth posts, and the second surface of the die is attached to the first surface of the heat sink.
24. The integrated circuit package of claim 23, further comprising a rectangular cavity formed in the first surface of the heat sink, wherein the second surface of the die is attached to a surface of the cavity.
25. The integrated circuit package of claim 24, wherein each corner of the cavity is adjacent to an inner corner of a corresponding one of the first, second, third, and fourth posts.
26. The integrated circuit package of claim 24, wherein each corner of the cavity forms a notch in a corresponding one of the first, second, third, and fourth posts.
27. The integrated circuit package of claim 23, wherein a depth of the recessed region between the first and second posts is less than a depth of the recessed region between the first and third posts.
28. A system for assembling integrated circuit packages, comprising:
- an extrusion press configured to extrude a stock material through a die to form a heat sink strip having a cross-section defined by the die, the die being configured to form a recessed region in a first surface of the heat sink strip along a length of the heat sink strip, and to form a plurality of fins in a second surface of the heat sink strip along the length of the heat sink strip; and
- a cross-cutter configured to cross-cut the heat sink strip to separate the heat sink strip into a plurality of heat sinks.
29. The system of claim 28, wherein the cross-cutter is configured to form a plurality of cross-cuts in the second surface of the heat sink strip across a width of the heat sink strip such that each heat sink separated from the heat sink strip includes at least one of the plurality of cross-cuts across a width of the heat sink.
Type: Application
Filed: Oct 30, 2008
Publication Date: Jan 28, 2010
Applicant: BROADCOM CORPORATION (Irvine, CA)
Inventors: Sam Ziqun Zhao (Irvine, CA), Calvin Wong (Irvine, CA)
Application Number: 12/261,407
International Classification: H01L 23/36 (20060101); H01L 21/98 (20060101);